Tuesday, August 05, 2008

The blind have a serious problem when it comes to hybrid cars. Since the gas engine shuts off when the hybrid car slows down or is stopped, there is no sound to warn them a hybrid car is there or is moving towards them. This has them so worried, they have petitioned the federal government and the individual state governments to pass an ordinance requiring vehicles to make a minimum amount of sound.

Lotus has introduced a new system to do just that. The nice part of the system is, while the gas engine is off, the sound system replicates the sound. But, if the gas engine kicks in, the sound system shuts itself off.

Lotus Engineering, the world renowned automotive consultancy division of Lotus, has developed technologies to synthesise external sound on electric and hybrid vehicles to counteract the growing concern these 'quiet' vehicles pose to pedestrians and cyclists. A simulation of a real engine sound is used on the 'Safe & Sound' Hybrid technology demonstrator vehicle, making it instantly recognisable that the vehicle is in motion.

Electric and hybrid vehicles, a favourite choice of the environmentally conscientious have recently come in for criticism from blind and partially sighted people. Due to the almost silent operation of hybrid vehicles at slower speed when running on electric power, the independent travel of the blind and partially sighted may be put at risk as they cannot hear these quiet vehicles as they approach, making crossing a road or walking through a car park hazardous.

The Lotus 'Safe & Sound' Hybrid technology demonstrator uses a standard Toyota Prius, one of the highest volume and most advanced hybrid vehicles to demonstrate the sound synthesis application and compensate for the lack of engine noise emitted by the vehicle when running on an electric motor. What has resulted is the same environmentally conscious hybrid vehicle, without the potential risk to pedestrians and cyclists.

The solution that Lotus has devised is a novel reapplication and development of its Sound Synthesis technology. This is a part of the Lotus suite of patented active noise technologies which comprise three main systems, Active Road Noise Cancellation, Engine Order Cancellation and Sound Synthesis.

To synthesise the engine sound, a road speed signal is taken from the vehicle and a waterproof loudspeaker system is positioned adjacent to the radiator allowing the sound to emanate from the front of the vehicle. Once the vehicle has passed, the sound is not heard. When the car is operating on the electric motor only, throttle and speed dependent synthesised sound projects a realistic engine sound in front of the vehicle. The technology was designed around the behaviour of a conventional engine, using an existing engine sound which makes it instantly recognisable with the pitch and frequency helping to identify vehicle distance and speed. If the hybrid's engine starts operating, at higher speeds or throttle demands or lower battery levels, the control system automatically stops the external synthesis. When the powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantaneously sets the system running again. It is all completely automatic and the driver hears almost none of the additional sound.

In order to generate the engine sound, recordings of a suitable donor engine were made and analysed to establish the characteristic frequencies at different engine speeds. These frequencies are then entered into the synthesis controller in the form of a 'voice' which outputs the sound through an amplifier and out through the loudspeakers.

1 comment:

tony regan
said...

After air pollution, noise pollution is the worst feature of conventional cars. How hellish to lobby governments to introduce laws to artificially produce it. Electric and hybrid cars do make noise in motion and our ears will soon be become attuned and used to detecting a lower and a different sound. Installing more pedestrian crossings would help the visually impaired, who generally have developed more acute hearing anyway.

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